In early May, I was part of a fact-finding trip to Japan. What I learned from four days of discussions with senior government officials, legislators and scholars was invaluable. I’ve worked with Japanese counterparts for many years, especially on issues related to North Korea, but what I took away from this trip was Japan’s deep concern about the existential nuclear threat from North Korea and the need for the U.S., working with Japan, to more aggressively pursue a resolution of this issue. What also got my attention was Prime Minister Shinzo Abe’s pro-active contribution to peace in the region and the real progress made with Japan’s commitment to collective defense with its U.S. ally.

Japan appreciates President Trump’s decision to make the North Korea nuclear threat a priority national security issue. For years, Japan has been living with this existential nuclear threat from North Korea. Now, the U.S. is seized with the reality that North Korea will soon become an existential nuclear threat to the U.S. The progress North Korea continues to make with its missile programs, definitely to include the recent Intermediate Range Ballistic Missile (IRBM) successes, with a mobile, solid fuel missile capable of reaching Guam, has correctly focused attention on the need to get North Korea to halt these missile launches and return to negotiations, ideally before they launch an Intercontinental Ballistic Missile (ICBM) capable of reaching the U.S.

Japan is supportive of President Trump’s strategy of “putting all options on the table.” Their preference would be returning to negotiations and getting China to use more of its leverage with North Korea to accomplish this goal. China’s decision to cease importing coal from North Korea in 2017 was movement in that direction. Another card available to China is the crude oil they provide to North Korea. Any reduction in the amount of oil China provides to North Korea would have immediate impact on the North’s economy and its ability to sustain its very vulnerable infrastructure.

A return to negotiations, however, must not only focus on halting North Korea’s nuclear and missile programs, it must also focus on our principal objective: Complete and verifiable denuclearization. There is a sense, and only a sense, that North Korea may believe that the progress they’ve made with its nuclear and missile programs has conditioned the international community to view a halt in these programs as the only realistic obtainable objective. Thus North Korea would retain its nuclear weapons and be accepted as a nuclear weapons state, albeit with a limited and capped nuclear weapons capability.

This would be a tragic mistake, not only for Japan and South Korea, but for the U.S. and those countries in the region. North Korea with even a few nuclear weapons would be a nuclear proliferation nightmare. Other countries, like South Korea, Japan, Taiwan, eventually may also decide that they need nuclear weapons, regardless of the U.S. nuclear umbrella. Also of concern has to be the accidental use of a nuclear weapon and the transfer, knowingly or accidentally, of a nuclear weapon or fissile material to a rogue state or terrorist organization.

The progress the U.S. is making in bringing Japan and South Korea together to address security issues with North Korea is impressive, and appreciated by Japan. This trilateral cooperation is a powerful message to Pyongyang that the U.S. and its two allies will work in tandem to address and ultimately resolve the nuclear issue with North Korea. The introduction of the Terminal High Altitude Area Defense (THAAD) in South Korea and the possible need for additional missile defense systems in Japan and in the region, depending on developments with North Korea, are issues Japan supports.

Finally, the U.S. decision to pull out of the Trans Pacific Partnership (TPP) was a disappointment to Japan. This will require, in my view, more of a U.S. effort to prove that we are committed to a real presence in the region and that our extended deterrence commitments to Japan are inviolable. China’s progress with its One Belt and One Road initiative and its investment and leadership in the Asia Infrastructure Investment Bank have captured the attention of Japan and others in the region, thus it’s only logical that the U.S. will have to do more to prove that we also are invested in and committed to the Asia-Pacific region for the long term.

• Joseph R. DeTrani was the former U.S. special envoy for negotiations with North Korea.